Nanoscale materials and unanswered questions on safety

Nanoscale materials and unanswered questions on safety

In recent years, efforts to develop the Next Big Thing — whether in medicine, computer technology, pollution prevention or high-performance materials — have turned to some really, really small things: nanomaterials.

Working at the nanoscale — which can mean the near-atomic scale, with substances a million times shorter than the length of an ant, a thousand times thinner than human hair — brings the ability to create new materials that can perform tasks in ways that might not otherwise be possible. But it also brings new concerns and challenges related to understanding environmental and human health impacts, because at the nanoscale, substances often take on chemical, biological and physical properties they might not otherwise have and behave in ways they might not at conventional sizes.

Nano in a nutshell

While definitions differ, nanomaterials typically measure in at a length, width, height or diameter of about 1 to 100 nanometers — 1 to 100 billionths of a meter. They take advantage of the physical, chemical and other characteristics substances exhibit at this minuscule size. At the nanoscale, materials can have different boiling points, different magnetic properties and different optical properties (color, fluorescence or transparency). They can conduct electricity or permeate and interact with living cells and other materials in ways they do not at larger sizes. And simply because they are so small, nanomaterials are capable of moving in ways and to places — whether in the environment or the human body — larger compounds cannot.

It’s because of these special properties that nanomaterials are being developed for so many applications. Not long ago the subject of science fiction (Michael Crichton’s "nanobots," for example), nanomaterials now can be found in a vast array of items. Some are being used to make extremely strong yet lightweight building materials, to efficiently store energy, to detoxify pollutants or to create antibacterial surfaces. Others are being used to deliver medical treatments to individual cells, to detect harmful bacteria or to create new ways of producing computer chips and semiconductors.

The U.S. Department of Agriculture is looking at how nanotechnology can be used to detect pathogens in poultry and is exploring ways nanomaterials might be added to edible food, said Bosoon Park, a lead scientist at the U.S. National Poultry Research Center. Using nanotechnology to detect harmful bacteria, Park said, significantly could reduce the time it takes to identify the source of an outbreak. In another application, researchers in Canada are harnessing the apparent ability of nanoparticles to remove highly persistent, toxic hydrocarbon compounds from oil sands wastewater.

Nanotechnology is often referred to as an 'emerging' technology, and we are a long way from fully understanding its toxicology and environmental impacts.

More mundanely, some of these properties are being harnessed to control odor in clothing such as socks and underwear, to deter microbes in plastic food containers and children’s stuffed animals, and to make sunscreens disappear more easily into your skin. The list of everyday and more specialized products in which nanomaterials are being used goes on: bicycles, cosmetics, personal care products and household appliances as well as electronics, aircraft and automotive parts, and pharmaceuticals. One database has logged more than 400 consumer products that contain nanosilver used as an antibacterial agent — just one of many nanomaterials used in products now on the market. Among these are toothpaste, pet and baby blankets, hair brushes, and a vacuum cleaner.

Small stuff, big questions

Nanotechnology is often referred to as an "emerging" technology, and we are a long way from fully understanding its toxicology and environmental impacts. But the same traits that make nanomaterials so uniquely useful also raise serious questions about their interaction with the environment, wildlife, our food supply and human bodies.

As the University of California Santa Barbara’s Center for Nanotechnology in Society noted, "These new nanotechnologies pose many uncertainties for society. The risks that may accompany their use are largely unknown [and may be] difficult to anticipate."

Some studies show that socks treated with nanosilver can release that silver when they’re washed. Others suggest that nanosilver can be released from plastics, including those used in food containers. Testing commissioned by the Center for Food Safety has found nanoparticles of titanium dioxide in numerous food products, including cheese, chocolate, candy and mayonnaise.

Because these particles are so small, there is concern they may behave in ways more toxic than their larger cousins. A whitening agent, titanium dioxide, is approved for use in food at the conventional size. The U.S. Food and Drug Administration, the federal agency that approves food additives, said it didn't yet know enough about materials engineered at the nanoscale to use them without special approval. Manufacturers of food in which the nanoscale titanium dioxide was found said these particles were not specially engineered or added but occurred unintentionally with those of conventional size. But because these particles are so small, there is concern they may behave in ways more toxic than their larger cousins. Right now European chemicals authorities are considering how to classify the carcinogenicity of titanium dioxide — including in its nano-form — a deliberation that could lead to its restriction in consumer products.

Some researchers are examining how ecosystems might be affected if nanosilver gets into soil and water sediment after products end up in the waste stream. Others have found that plants can absorb nanosilver in minute quantities if it’s present in the soil. As the U.S. Environmental Protection Agency explains on its website, evaluating the toxicity of nanomaterials "is difficult because they have unique chemical properties, high reactivity and do not dissolve in liquid" and because existing tests "may not work to test the safety of nanomaterials."

Researchers at the University of Minnesota Twin Cities and University of Wisconsin-Milwaukee working with the Center for Sustainable Nanotechnology are exploring whether nanomaterials affect gene expression. The aim is to learn about how "sub-lethal" exposures might set the stage for later health problems. Given nanomaterials’ ability to penetrate cells, this seems particularly important.

“There are big questions about toxicity,” said Park.

There is also concern that, given their size, nanomaterials can penetrate skin and cells in ways larger materials cannot. Numerous studies have been looking at these effects as a result of occupational exposure, environmental exposure and exposure to consumer products containing nanomaterials. One recent study has found engineered carbon nanotubes in children’s lungs, particles that apparently were present in the mix of other air pollutants. These tiny tubular particles pose concerns because of their ability to penetrate lung tissue and cause respiratory problems. Other research has noted carbon nanotubes’ similarity to asbestos fibers, and researchers are investigating if these nanomaterials can affect lung tissues in the same way asbestos does — causing scarring and inflammation that can lead to lung cancer, mesothelioma and asbestosis.

Risks: unknown

Adding to the inherent challenge of understanding the life-cycle impacts of these products is that the proliferation of nanomaterials and products containing them appears to be outpacing any systematic cataloguing or labeling of these products. Put simply, we don’t know exactly where and how they’re being used.

That means that in addition to not fully understanding nanomaterials’ hazards, the risks of exposure are also not yet well understood. "Until we understand what realistic environmental concentrations [of nanomaterials] are likely to be, we don’t really know what the impacts are," said University of California, Santa Barbara, Bren School of Environmental Science & Management doctoral candidate Kendra Garner, who is studying ways of measuring nanomaterials’ environmental effects, including developing a special statistical model that will help with these estimations.

"It’s very complicated," said Garner. “There are not really techniques at this point to measure nanomaterials in situ in the environment.” Even if researchers are able to take samples, "by the time you get to the lab they may have changed because they are so reactive. It’s even harder to figure out where they come from."

When considering potential environmental or health impacts of nanomaterials, National Nanotechnology Initiative deputy director Lisa Friedersdorf said it’s important to understand that "in very few applications are you talking about individual nanoparticles." Rather, she explained, they’re more often "part of a system."

While a particular nanomaterial might not pose concerns in a finished consumer product, it might still have "worker implications" during manufacturing.In electronics, for example, "nanofeatures may be wires that are really tiny or transistors that have features that are at the nanoscale," she explained. The same thing is true of super-hydrophobic coatings that are stain or mud resistant — materials that use compounds at the nanoscale to make a texture that creates the desired performance. There are, however, some applications in which individual nanoparticles perform the job — in medicine, for example, where they can be used to home in on individual cells whether as a diagnostic tool or a pharmaceutical.

But as Center for Food Safety senior policy analyst Jaydee Hanson observed, while a particular nanomaterial might not pose concerns in a finished consumer product, it still might have worker implications during manufacturing.

Knowledge gap meets regulatory chasm

As the proliferation of nanomaterials continues and scientists try to get a handle on their potential human and environmental health effects, regulators are facing their own challenge: How to manage materials that don’t behave like those that existing chemicals policies were designed to deal with.

The European Union has required labeling for nanomaterials used as antibacterials and in cosmetics since 2013. Under its new "novel food" regulation, the EU also will require prior approval of engineered nanomaterials used in food and may require special labels if the food "is not recommended for certain vulnerable groups" such as infants, children or pregnant women.

The U.S., on the other hand, has no labeling requirements of any kind to specify that products contain nanomaterials. In fact, the U.S. federal agencies that oversee chemical ingredient safety — primarily the EPA and the U.S. Food and Drug Administration — treat nanomaterials as they would any other new chemical on a case-by-case basis rather than singling them out for special scrutiny of any kind because of their size.

Simply put, we don’t know enough about nanomaterials to know if standard health and safety measures will be effective.

Simply put, we don’t know enough about nanomaterials to know if standard health and safety measures will be effective. This, said Hanson, can pose problems, because it means using regulatory "tools to do jobs they weren’t necessarily intended to do." For example, because nanoparticles are so small and behave so differently than larger particles, equipment that ordinarily would be used to clean up an indoor spill or protect workers from inhaling particles won’t necessarily work on them. Similarly, nanomaterials’ size means they can’t be treated as other environmental contaminants might be in terms of pollution prevention. At the same time, assumptions about how chemicals will behave once in products won’t necessarily apply to nanomaterials. Currently, there is "a growing concern about the lack of environmental health and safety data" (PDF), said the EPA.

Simply put, we don’t know enough about nanomaterials to know if standard health and safety measures will be effective or if we’re asking the right questions about these new materials to make sure they will be used safely.

Push for oversight

The lack of regulations requiring labeling or other listing of these materials also means the U.S. is without any official inventory of products containing nanomaterials. Currently, the most comprehensive catalog in terms of product categories is one compiled by the Project on Emerging Nanotechnologies, a joint initiative of the Pew Charitable Trusts and the Woodrow Wilson International Center. Another database of products containing nanomaterials was recently launched by the Center for Food Safety and focuses on food and food-contact products. Some products listed in both inventories make explicit claims for their nanotechnology — such as carbon nanofiber materials in sports gear or nanosilver used as an antimicrobial agent in clothing or food containers — but others do not.

"This makes it a confusing situation for consumers," said Wilson Center Science and Technology Innovation Program senior associate Todd Kuiken. And, said Kuiken, it’s very possible that a company may not know the details of the nanotechnology used in its products because it may have purchased ingredients or other components for which full details of proprietary formulas or technology may not have been disclosed. This also adds to the difficulty in understanding these products’ potential environmental and health impacts.

Environmental and consumer advocates said the EPA is not keeping close enough tabs on how nanomaterials are being used.

For example, the Center for Food Safety, Beyond Pesticides, Clean Production Action, Center for Environmental Health and other groups filed suit against the agency asking it to regulate all uses of nanosilver as it would a pesticide or another antimicrobial chemical. Under existing regulations, the EPA is responsible for granting approval of materials that make antibacterial claims. So if a manufacturer explicitly said its food containers will "kill germs" or its fabric treatment will "destroy microbes," these products are supposed to be registered with and individually approved by the EPA. But, claim the groups involved in the lawsuit, when it comes to products containing nanosilver, the EPA has failed to adequately enforce these regulations, allowing products containing nanosilver — but not making specific germ-killing claims — to be sold without EPA approval.

The U.S. Consumer Product Safety Commission has been taking a hard look at some consumer products containing nanomaterials. Back in 2008, these groups filed a legal petition with the EPA asking it to take such action. Six years later, the EPA had failed to respond — so in December 2014, the groups filed suit against the EPA both for the EPA’s failure to respond to their petition and to again ask the EPA to fully regulate nanosilver as a pesticide. In March (PDF) the EPA agreed that nanosilver products sold with the intent of killing microorganisms do qualify as pesticides. But it refused the groups’ request to automatically consider all nanosilver products as pesticides — including those that don’t make explicit germ- or bacteria-killing claims.

At the same time, however, since 2011 as part of the National Nanotechnology Initiative — funded at $1.6 billion in the 2016 federal budget — the U.S. Consumer Product Safety Commission has been taking a hard look at some consumer products containing nanomaterials. With other federal agencies, including the EPA, FDA and National Institute for Occupational Safety and Health, the CPSC has been working to develop ways of assessing the potential airborne release of nanoparticles from various consumer products — among them aerosol sprays, sports equipment and products that might pose special exposures to children.

And while there doesn’t appear to be any federal move afoot to require labeling of nanomaterials in products sold in the U.S., the Environmental Working Group has launched an initiative involving personal care products and cosmetics asking manufacturers to add product toxicity details to the information visible to consumers either in stores, on packages or online. Companies that stay with the program for a year also will be asked to disclose ingredients on labels in a way that conforms with EU requirements — which would include disclosing use of nanomaterials. The hope is this will help create consumer demand for other companies to follow suit. Such pressure for ingredient disclosure has led to passage of state chemical reporting and GMO labeling laws.

And the groups that have been pushing the EPA for more rigorous oversight of nanosilver products are also pushing the agency on its review of other nanomaterials, including a nano-silica compound that’s being developed for use in plastics, said Center for Food Safety’s Hanson.

The bottom line

So what is the bottom line on nanotechnology’s impacts on human health and the environment?

Essentially, we don’t yet know. On the one hand, nanotechnology applications offer many promising solutions, whether in pollution prevention, medicine, water treatment, electronic and energy production or countless other areas. On the other hand, much science is emerging to suggest these materials present potential environmental and health hazards. And right now nanomaterials are not being fully catalogued, monitored or regulated, which only adds to the challenges of understanding their environmental impacts.

In other words, the application of very, very small technologies still carries some very big questions about where these materials are being used, how they are behaving and what we need to do to protect ourselves and the rest of the planet against unwanted impacts and exposures.